The present invention relates to a drilling assembly for producing boreholes having undercut or enlarged portions.
Drilling assemblies of the type under discussion have been known. One of such assemblies has been disclosed in the German Patent DE-PS No. 3,037,408. The drilling assembly disclosed in this patent enables, in a simple fashion, the drilling of bores having an undercut at the base of the bore by pivoting the drill after the latter has reached a desired depth of the bore. The pivotable support of the drill receiver makes it possible to pivot the drill at the predetermined depth of the bore such that the drill head reames or countersinks conically the borehole base. Special anchoring elements may be inserted in the borehole formed in such a manner. These anchoring elements can spread out in the region of the borehole base so that a form-locking connection between the anchoring element and the wall of the borehole takes place.
Known drilling assemblies are utilized particularly for making boreholes in masonry of concrete. The head of the drill which has a greater diameter than that of the drill shank or shaft is subject to higher wear, whereby with increasing operation duration the diameter of the drill head is reduced and thus the boreholes produced thereby become of smaller diameter. A centering attachment provided on and extending outwardly from the housing of the conventional drilling assembly is adjusted in its outer diameter to a minimal borehole diameter produced. This results in that the centering attachment, particularly when a new drill is utilized, which produces the borehole of a greater diameter, is not able to precisely center the drill in the borehole. Thus countersinking or reaming the undercut is made quite difficult.